Automatic current transformer polarity correction

Abstract

A method of processing current transformer data, performed by an electronic trip unit, includes obtaining first current data based on a first current signal from a first current transformer, second current data based on a second current signal from a second current transformer, and third current data based on a third current signal from a third current transformer. Using the current data, it is determined whether one of the current transformers is connected to the electronic trip unit with an improper polarity. Upon determining that one of the current transformers is connected to the electronic trip unit with an improper polarity, the obtained current data corresponding to the current transformer that is connected with improper polarity is automatically inverted. A ground fault calculation is performed using the automatically inverted current data.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]Embodiments of the present invention relate to electrical overcurrent protection devices, and in particular to electronic trip units for circuit breakers.[0003]2. Description of Related Art[0004]Circuit breakers are used in electrical distribution systems to protect electrical conductors and equipment against the effects of short circuits, ground faults, overloads and / or overcurrent conditions (collectively “abnormal current conditions”). Some circuit breakers have programmable electronic controllers for controlling operations of the circuit breaker. The programmable electronic controllers are known as electronic trip units and circuit breakers employing electronic trip units are known as electronic trip circuit breakers. The electronic trip unit monitors the conditions of an electrical circuit protected by its associated circuit breaker, and signals the circuit breaker to trip upon detecting an abnormal current conditi...

AI Technical Summary

Benefits of technology

The patent describes a method and system for detecting and responding to ground faults in a circuit breaker system. It uses current transformers to measure the current in each phase of a three-phase electrical circuit. The system analyzes the data from these transformers to determine if there is an improper polarity current transformer connected to the system. When an improper transformer is detected, the system automatically inverts the data from it and performs a ground fault calculation. The system then sends a trip command to a circuit breaker actuator to open the circuit in response to the detected fault. The technical effect of this invention is to increase the accuracy and reliability of identifying and responding to ground faults in a circuit breaker system.

Problems solved by technology

Current transformers have a polarity, and it is possible to improperly install a current transformer in the electrical circuit.

Installing CTs with an improper polarity can result in nuisance ground fault tripping until the improperly installed CTs are discovered and corrected.

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